A Method and Apparatus for Modulating and Demodulating Data into a Variable-Length Code and Providing a Sync Signal to the Train of Codes

1. A data-modulating method of modulating data having a basic data length of m bits, to a variable-length code (d, k; m, n; r) having a basic code length of n bits, said method including the steps of: receiving a train of codes; and adding a sync signal to said train of codes after a minimum run, said sync signal having a pattern that breaks a maximum run, wherein said pattern is repeated twice continuously, wherein said minimum run is repeated no more than six times; and wherein said sync signal exhibits seven types of sync signal IDs, and any adjacent two bits of a sync signal ID are spaced apart by a distance of 2.